(NOT APPLICABLE)
1. Field of the Invention
The present invention relates to measurements of oxygen saturation and concentrations of hemoglobins in arterial blood by using a pulse oximeter, and more particularly to measurement of a concentration of methemoglobin (MetHb).
2. Related Art
A conventional pulse oximeter is constructed such that near-infrared rays of light and red rays of light are irradiated onto a living tissue, ratios of the pulsating components of attenuations of these lights having passed through the living tissue are processed, and an arterial oxygen saturation is noninvasively measured from the result of the processing.
The measuring principle of the pulse oxometer is known as disclosed in JP-A-53-26437, proposed by the applicant of the present patent application. The measuring principle of the pulse oximeter will be described in brief hereunder.
For example, suppose a living tissue R is divided into a blood layer R1 and a layer R2 of a tissue other than blood this tissue will be referred to as a pure tissue), and it is assumed that a thickness of the blood layer R1 is pulsated, but a thickness of the pure tissue layer R2 is not pulsated, viz., it is constant. Where the living tissue R is irradiated with light, an incident light amount IO is reduced by the living tissue R, and an amount of light passing through the living tissue R is I. when a thickness of the blood layer R1 is pulsated to be increased by xcex94Db, the amount of the transmitted light is reduced to be (Ixe2x88x92xcex94I). In this case, an attenuation xcex94A of the light, which is produced by a thickness change xcex94Db of the blood layer R1, is given by
xcex94A=log [I/(Ixe2x88x92xcex94I)]
When lights of different wavelengths xcex1 and xcex2 are irradiated onto the living tissue R, a ratio "PHgr" of attenuations xcex94A1 and xcex94A2 of lights of the wavelengths xcex1 and xcex2, which are produced by the pulsation of the tissue thickness is mathematically approximated by
xe2x80x83"PHgr"=xcex94A1/xcex94A2={square root over ( )}{E1(E1+F1)}/{square root over ( )}{E2(E2+F2)}xe2x80x83xe2x80x83(1)
This is theoretically and empirically confirmed.
In the above expression, Ei is an absorption coefficient of hemoglobin, Fi is a scattering coefficient of light in blood, and i=1, 2, which represent the wavelengths xcex1 and xcex2. Assuming that light absorbing materials in blood are only oxyhemoglobin and deoxyhemoglobin, then the absorption coefficient Ei of the hemoglobin is given by the following expression.
Ei=SEOi+(1xe2x88x92S)Erixe2x80x83xe2x80x83(2)
In the expression, S is an oxygen saturation, and Eoi is an absorption coefficient of oxyhemoglobin and Eri is an absorption coefficient of deoxyhemoglobin. Substituting the expression (2) for the expression (1), then we have the following expression
"PHgr"=xcex94A1/xcex94A2={square root over ( )}[{SEo1+(1xe2x88x92S)Er1}[{SEo1+(1xe2x88x92S)Er1}+F1]]/{square root over ( )}[{SEo2+(1xe2x88x92S)Er2}[{SEo2+(1xe2x88x92S)Er2}+F2]]xe2x80x83xe2x80x83(3)
In the expression (3), Eol, Er1, Eo2, Er2 F1 and F2 are known values. Therefore, an oxygen saturation S can be obtained in a manner that "PHgr"=xcex94A1/xcex94A2 is measured, substituted for the expression (3), and the expression is solved for the S.
If methemoglobin MetHb is present in blood, a drop arises in a reading of a degree of oxygen saturation measured by a related-art pulse oximeter using two wavelengths; that is, near-infrared rays of light and red rays of light. Since the oximeter cannot determine a concentration of methemoglobin MetHb, the presence/absence or concentration of methemoglobin MetHb in blood (also called a xe2x80x9cblood methemoglobin MetHb concentrationxe2x80x9d) remains uncertain until blood of interest is sampled and subjected to measurement performed by a carbon monoxide oximeter (CO-Oximeter).
Meanwhile, where the arterial blood pulsates, the theory teaches that concentration ratios of xe2x80x9cnxe2x80x9d number of light absorbing materials in the blood can be measured by using xe2x80x9cnxe2x80x9d number of wavelengths of lights. Accordingly, the theory also teaches that it is impossible to measure concentration ratios of three hemoglobins, oxyhemoglobin O2Hb, deoxyheoglobin RHband methemoglobin MetHb by using two wavelengths of lights, and at least three wavelengths must be used for the measurement.
Actually, however, the influence by pure tissues other than the blood will produce measuring errors. Accordingly, to accurately measure concentrations of xe2x80x9cnxe2x80x9d number of light absorbing materials in the blood, it is preferable to use (n+1) number of wavelengths, this fact was found and confirmed by us. The applicant of the present patent application developed an apparatus for determining concentrations of materials in blood based on the above fact, and filed the patent application on the apparatus (JP-B-5-88609). Other light absorbing materials, such as carboxyhemoglobin (COHb) and bilirubin, are also contained in the blood. To remove the influence by those materials is attempted, the number of wavelengths used is further increased, and further cost to manufacture the apparatus is also increased.
In adding a third wavelength for measuring the methemoglobin Metub to the pulse oximeter (JP-A-5-228129), the ratio of absorption coefficients of oxyhemoglobin O2Hb and methemoglobin MetHb at the wavelengths of lights, which are longer than the red wavelengths, as shown in FIG. 11, is almost constant. For this reason, where the third wavelength is selected from those wavelengths longer than the red wavelengths it is very difficult to determine the methemoglobin MetHb concentration sensitively.
Scharf proposed in his patent (U.S. Pat. No. 5,830,137) the use of the green wavelength region for the third wavelength. The absorption coefficient of every kind of hemoglobin, as shown in FIG. 11, is considerably large in the yellow and green wavelength regions. The absorption coefficients of the oxyhemoglobin O2Hb in the wavelength region of 500 nm to 620 nm are at least 10 times as large as those at 660 nm. Light having passed through the blood is very weak, and the measurement at good S/N ratio is very difficult.
Accordingly, an object of the present invention is to provide an apparatus for determining concentrations of hemoglobins which, using an orange or red orange wavelength region for the third wavelength in addition to the near-infrared and red wavelength regions, which are conventionally used, can detect a change of the transmitted light by a change of the methemoglobin MetHb at good S/N ratio, and can easily discriminate between the methemoglobin Metab and the deoxyhemoglobin RHb, and hence can perform a proper measurement of methemoglobin MetEb.
The present invention provides an apparatus for determining concentrations of hemoglobins according to the present invention comprises:
a light source which emits at least three different light rays: that is, light in a near-infrared wavelength region as a first wavelength, light in a red wavelength region as a second wavelength, and light in a red orange wavelength region as a third wavelength;
light-receiving means for receiving light that has originated from the light source and has passed through or has been reflected by a living tissue;
attenuation ratio processing means which processes an attenuation ratio "PHgr" between the light rays of the wavelengths in accordance with a change in a received-light output signal in each wavelength output from the light-receiving means as a result of pulsation of blood; and
concentration ratio processing means which processes at least concentration ratios of oxyhemoglobin and that of methemoglobin.
In this case, the concentration ratio processing means can be configured so as to process a proportion between an ever-changing concentration of oxyhemoglobin, an ever-changing concentration of methemoglobin, and an ever-changing concentration of methylene blue when medical treatment of methemoglobinemia is performed by administration of methylene blue into a living tissue, provided that at least a concentration of deoxyhemoglobin and that of carboxyhemoglobin remains unchanged.
Preferably, the apparatus can also be configured so as to further comprise oxygen saturation processing means which processes a functional oxygen saturation or a fractional oxygen saturation on the basis of an output from the concentration ratio processing means.
Preferably, the apparatus can also be configured so as to further comprise alarm display means for displaying an alarm in accordance with a level of the concentration ratio of methemoglobin obtained by the concentration ratio processing means.
Preferably, the apparatus can also be configured so as to further comprise event input means for enabling event entry at the time of occurrence of event information about medical treatment or about a patient; and storage means for storing a time at which input information is entered by way of the event input means, the event information, and a result of processing performed by the concentration ratio processing means.
Preferably, the apparatus can also be configured so as to further comprise display means which provides the processing result in the form of a trend display and which provides the event information stored in the storage means in the form of the trend display at a corresponding time.
Preferably, the apparatus can also be configured so as to further comprise an interface which transmits the event information, the time, and the processing result, all being stored in the storage means, to an external device.
The present invention also provides an apparatus for determining concentrations of hemoglobins, comprising:
a light source for emitting a plurality of light rays of different wavelengths;
light-receiving means for receiving light which has originated from the light source and has passed through or been reflected by a living tissue;
calibration value input means for entering a concentration of at least one type of light-absorbing material in blood;
attenuation ratio processing means for processing an attenuation ratio "PHgr" between the light rays of the wavelengths, on the basis of a change in a received-light output signal in each wavelength output from the light-receiving means as a result of pulsation of blood; and
concentration ratio processing means for processing a concentration ratio of oxyhemoglobin and a concentration ratio of methemoglobin, on the basis of an output from the attenuation ratio processing means and of the concentration of light-absorbing material input by way of the calibration value input means. Further, the apparatus can be also configured so as to comprise storage means for storing data pertaining to the attenuation ratio "PHgr"; and concentration ratio processing means for retroactively re-processing at least a concentration ratio of oxyhemoglobin and a concentration ratio of methemoglobin, through use of the data stored in the storage means and the concentrations of light-absorbing materials in blood entered by way of the calibration value input means.
The present invention also provides an apparatus for determining concentrations of hemoglobins, comprising:
a light source for emitting a plurality of light rays of different wavelengths;
light-receiving means for receiving light which has originated from the light source and has passed through or been reflected by a living tissue;
attenuation ratio processing means for processing an attenuation ratio "PHgr" between the light rays of the wavelengths, on the basis of a change in a received-light output signal in each wavelength output from the light-receiving means as a result of pulsation of blood;
concentration ratio processing means for processing at least a proportion between a concentration of oxyhemoglobin and a concentration of methemoglobin, on the basis of an output from the attenuation ratio processing means; and
select means for instructing process of a concentration ratio of methemoglobin,
wherein, when the select means has not yet instructed process of a concentration ratio of methemoglobin, the concentration ratio processing means processes a concentration ratio of at least oxyhemoglobin, on the basis of variations in received-light output signals output as a result of the light-receiving means having received at least two different light rays which have originated from the light source and have passed through or been reflected by the living tissue; and
wherein, when the select means has instructed process of a concentration ratio of methemoglobin, the concentration ratio processing means processes concentration ratios of at least oxyhemoglobin and methemoglobin on the basis of variations in received-light output signals output as a result of the light-receiving means having received at least three different light rays which have originated from the light source and have passed through or been reflected by the living tissue
The present invention also provides an apparatus for determining concentrations of hemoglobins, comprising:
a light source for emitting a plurality of light rays of different wavelengths;
light-receiving means for receiving light which has originated from the light source and has passed through or been reflected by a living tissue;
attenuation ratio processing means for processing an attenuation ratio "PHgr" between the light rays of the wavelengths, on the basis of a change in a received-light output signal in each wavelength output from the light-receiving means as a result of pulsation of blood;
concentration ratio processing means for processing at least a proportion between a concentration of oxyhemoglobin, a concentration of deoxyhemoglobin, and a concentration of methemoglobin, on the basis of an output from the attenuation ratio processing means; and
display means for displaying the determined value of oxyhemoglobin, that of deoxyhemoglobin, and that of methemoglobin through use of two-dimensional coordinates.
Preferably, the apparatus for determining concentrations of hemoglobins can be configured such that the light source emits at least three light rays of different wavelengths: that is, light in a near-infrared wavelength region as a first wavelength, light in a red wavelength region as a second wavelength, and light in a red orange as a third wavelength.
An apparatus for determining concentrations of hemoglobins according to the present invention comprises:
a light source which emits at least three different light rays: that is, light in a near-infrared wavelength region as a first wavelength, light in a red wavelength region as a second wavelength, and light in a red orange wavelength region as a third wavelength;
light-receiving means for receiving light that has originated frog the light source and has passed through or has been reflected by a living tissue;
attenuation ratio processing means which processes an attenuation ratio "PHgr" between the light rays of the wavelengths in accordance with a change in a received-light output signal in each wavelength output from the light-receiving means as a result of pulsation of blood;
concentration ratio comparison means which processes at least a proportion of the concentration of oxyhemoglobin, that of carboxyhemoglobin, and that of methemoglobin; and
switch means for causing the concentration ratio processing means to selectively process a ratio of the concentration of carboxyhemoglobin to that of methemoglobin.
In this case, the apparatus for determining concentrations of hemoglobins can be constructed such that a predetermined threshold is set for an attenuation ratio to be processed by the attenuation ratio processing means; and there is provided display means for displaying an alarm when an attenuation ratio processed for the hemoglobin to which the switch means has been switched has exceeded the threshold value.
The present invention also provides an apparatus for determining concentrations of hemoglobins according to the present invention comprises;
a light source which emits at least three different light rays: that is, light in a near-infrared wavelength region as a first wavelength, light in a red wavelength region as a second wavelength, and light in a red orange wavelength region as a third wavelength;
light-receiving means for receiving light that has originated from the light source and has passed through or has been reflected by a living tissue;
attenuation ratio processing means which processes a ratio of an attenuation associated with concentrations of carboxyhemoglobin and methemoglobin on the basis of a variation of a received-light output signal in each wavelength output from the light-receiving means as a result of pulsation of blood; and
display means for displaying an alarm when at least either a processed attenuation ratio of carboxyhemoglobin or a processed attenuation ratio of methemoglobin has exceeded a range of a predetermined threshold value, the threshold value being set for an attenuation ratio of carboxyhemoglobin and an attenuation ratio of methemoglobin which are to be processed by the attenuation ratio processing means.
Preferably, at least the first wavelength is selected from a near-infrared wavelength region of 790 to 1000 nm; the second wavelength is selected from a red wavelength region of 640 to 675 nm; and the third wavelength is selected from a red orange wavelength region of 590 to 660 nm.
Particularly, the third wavelength is preferably set to 621 nm.
The present invention also provides an apparatus for determining concentrations of hemoglobins, comprising:
a light source for emitting a plurality of light rays of different wavelengths;
light-receiving means for receiving light which has originated from the light source and has passed through or been reflected by a living tissue;
input means for entering a reference time;
attenuation ratio processing means for processing an attenuation ratio "PHgr" between the light rays of the wavelengths, on the basis of a change in a received-light output signal in each wavelength output from the light-receiving means as a result of pulsation of blood; and
concentration variation processing means for processing variation in the concentration of at least either carboxyhemoglobin or methemoglobin having arisen since the reference time entered by way of the input means.
By means of this configuration, a physician who performs medical treatment performs an input operation for causing the apparatus to recognize, e.g., when the treatment is initiated, as a reference time by way of the input means. There can be processed variation in the concentration of at least either carboxyhemoglobin or methemoglobin having arisen since the reference time input by way of the input means.
Moreover, the input means corresponds to calibration value input means; and the concentration variation processing means processes variation in a concentration having arisen since the reference time, by inputting a tentative value by way of the calibration value input means as a concentration of light-absorbing material in blood.
As a result, provided that time when a medical treatment has been initiated is taken as a reference time, there can be processed variation in the concentration of carboxyhemoglobin or methemoglobin having arisen since the reference time, by inputting a tentative value by way of the calibration value input means as a concentration of light-absorbing material in blood.